Looking for a thorough responce

to sum it down dad is hazy about letting me build a computer myself with all the parts ordered for cheaper online even though I've spent months now proving to him anything he sees at sams/walmart/circuit city/ is cheaper sometimes LOTS cheaper when built yourself. Also I would have to pay for itmyself and work until christmas cause my bank account is nil. Though if hes willing to buy this computer with his $$ should I let cheap go along with it or can I OFFER to do better building one myself? http://www.ubid.com/HP_Pavilion_a6152n_Core_2_Quad_Q6600_2.4_GHz_3GB_400GB/a11192184.html
is it a good deal or not? If I can spend like 400 dollars just upgrading the video card from the integrated one are the parts in it for what it has check RAM/CPU/ mobo is always undisclosed for some reason, is it worth the price tag ?